The present invention relates to an energy management system, in particular an automotive regenerative propulsion system for generating and accumulating propulsion energy by retardation of movement. The system has particular application to heavy land haulage vehicles, such as prime movers, and it will be convenient to describe the invention in relation to that particular application. However, it is to be understood that the invention has wider application such as to other types of automotive vehicles, such as light trucks, buses and cars.
Regenerative propulsion systems are known and have been applied to trucks and buses in the past. Such systems harness energy by retarding the vehicle under braking conditions and accumulating that energy for later use to propel the vehicle. The known systems have however lacked flexibility in their operation, as they principally have been arranged to dump accumulated energy all at once, for example when a vehicle is accelerating from a standing start, while those systems that have allowed for more controlled release of stored energy, have not done so to optimum efficiency. The use of the energy in the known systems is therefore somewhat inefficient and the known systems therefore have not met with widespread use. Additionally, known systems are time consuming and labor intensive to install.
It is an object of the present invention to provide an improved regenerative propulsion system. It is a further object of the invention to provided a system that can be controlled to generate and release retarding energy more efficiently than known systems. It is a further object to provide a system that is relatively easy and quick to fit to a vehicle.
According to the present invention there is provided an energy management system operable in three modes of operation to either drive or retard the drive shaft of a vehicle, or in a neutral mode, to have no driving or retarding influence on the drive shaft, said, system including energy accumulating means which is operable to store and release energy through receipt and release of fluid, pumping means in fluid communication with said energy accumulating means, a reservoir fluid in communication with said pumping means, and coupling means for coupling said pumping reads to said drive shaft, whereby in said retarding mode of said system, said drive shaft drives said pumping means to pump fluid to said energy accumulating means, and whereby in said driving mode of said system, said energy accumulating means releases fluid to drive said pumping means which drives said drive shaft, and whereby in said neutral mode of said system, said pumping means is inoperative to exert any driving or retarding influence on said drive shaft.
As defined above, the system is applicable to or forms a replacement of the drive shaft of a vehicle. However, it is envisaged that the system could also be applied to a shaft that is not directly or indirectly driven, by the engine of a vehicle, but instead, the shaft may be the axle of a trailer and as such, the term xe2x80x9cdrive shaftxe2x80x9d is therefore to be understood as embracing other such shafts to which the invention could be applied.
The drive shaft, or other shaft to which the system is applied, can operate independently of the system when appropriate by choosing the neutral mode of the system, however, rotation of the shaft can be assisted by system propulsion or retardation when appropriate. Thus, the system can exert greater control over the accumulation or dissipation of energy, by accumulating or releasing that energy when it is most desirable to do so, and not simply when it is possible to do so, such as in the prior art.
The system is coupled to the relevant shaft in any suitable manner, and in one arrangement, that coupling is made intermediate two sections of the shaft. For such an arrangement, the drive shaft may be provided in part, by two sections which are spaced apart to define opposed shaft ends and the system is provided between and connected to those two sections. For connection, the system may include a main shaft that is connectable to the opposed shaft ends by suitable means such as yoke connectors which are commonly employed between the drive shaft and the differential and gearbox described above, or it may include a full length drive shaft so that the system may be fitted to an existing vehicle simply by removing the existing drive shaft and replacing that with the drive shafts of the system. However other arrangements may also be employed.
In either arrangement described above, the drive shaft of the system can be driven or retarded so that the driving or retarding force applied thereto is transferred to the vehicle drive line and consequently the vehicle is driven or retarded accordingly. That drive or retard force is provided as an assistance to any drive and retarding systems which already form part of the vehicle, namely engine drive and braking systems and mechanical braking systems. Thus, the drive or retard force applied by the system may only be a portion of the overall drive or retard force applied to the vehicle.
It is however possible that the system apply the full drive or retard force, if the force required is within the available limits of the system. For example, the retard force available to be provided by the system may be sufficient to provide the sole retarding force to the vehicle, particularly in such situations when the vehicle is being retarded only slightly to maintain a constant speed on a downhill decline. In the reverse, it is not envisaged that the vehicle will be driven solely by the propulsion energy stored by the system, but that could occur if necessary.
In a first form of the invention, the coupling means of the energy management system includes an auto sequential gearbox that can drive the drive shaft of the system or which can be driven by the drive shaft depending on the mode in which the system is operating. This gearbox includes at least a pair of gears mounted on a second shaft that mesh with gears fitted to the main shaft. The pairs of meshed gears provide different ratios of drive and a selector facility is provided for manual or automatic selection of gear engagement depending on the ratio of drive or retardation required. The selector facility is preferably controlled electro-pneumatically, such as by a selector shaft controlled by a solenoid operated pneumatic actuator which moves laterally to the rotational plane of the gears and which includes means selectively engagable with one of the two pairs of meshed gears for transmitting drive. That engagement means may take any suitable form although it preferably includes a clutch mechanism, such as a dog clutch
The auto sequential gearbox is connected to pumping means comprising a pump/motor arrangement that is driven by the second shaft and that operates as a pump in system retard mode and as a motor in system drive mode. The connection between the second shaft and the pumping means can be made by any suitable connection arrangement. The pump arrangement preferably employs a hydrostatic pump with variable displacement, so that the output of the system can be manually or automatically adjusted. For this purpose, the pump is preferably an axial piston pump which employs a tiltable swash plate that can be manually or automatically manipulated.
In an alternative form of the invention, the energy management system includes a complete drive shaft and connecting means, such as a pair of yokes disposed at either end of the drive shaft for connection of the drive shaft, between the gearbox and the differential of a vehicle. In this form of the invention, when the system is installed, the drive shaft of the system forms the drive shaft of the vehicle. This arrangement therefore differs from the first form of the invention, in which the system employs a main shaft that forms a section of the overall drive shaft. Between the yokes on the drive shaft, one or more pump assemblies are coupled to the shaft by coupling means and are driven by the shaft in the retard mode of the system, or drive the shaft in the drive mode of the system. The pumps are arranged or selected to provide no driving or retarding influence in the neutral mode of the system.
The pump or pumps which are coupled to the drive shaft may be coupled thereto in any suitable manner and in one form of the invention, the drive shaft is splined for splined connection with rotating parts of the pumps. In this arrangement, the shaft may drive the pumps through the splined connection, or may be driven by that connection.
The or each pump is again, in this form of the invention preferably of a variable displacement, hydrostatic kind, that employs a tiltable swash plate which can be manually or automatically manipulated. If more than a single one of these pumps is fixed so the drive shaft, the pumps preferably connected in series along the shaft between the yokes. Open circuit axial piston pumps can readily be employed in this arrangement although the pumps could alternatively comprise radial piston pumps.
An assembly of the above kind comprising a plurality of pumps preferably employs internal porting providing communication between adjacent pumps. External porting car be provided at either end of the assembly of pumps for ingress and egress of fluids. In an arrangement that employs two or more pumps, the adoption of internal porting permits the use of minimal external porting, so as to minimise the number of hydraulic hoses connected to the assembly. In one arrangement, the assembly employs external porting in the form of a single front port and two rear ports, the front port communicating with an outlet of the fluid reservoir, and the rear ports being in communication respectively with an inlet of the fluid reservoir and the energy accumulation means. Alternatively, the rear port in communication with the inlet of the fluid reservoir can communicate with the inlet of a cooling system which in turn communicates with the fluid reservoir. In most forms of the energy management system, a cooling system is necessary for cooling the fluid being pumped.
In a preferred form of the invention, fluid pressure to or from the pump arrangement is controlled by balanced logic control elements to maintain separate constant pressure rating between the pump assembly, the fluid reservoir and the accumulation means.
The pump arrangement of the invention is preferably connected by suitable hydraulic lines to the fluid reservoir. The cooling system (if provided) and to the energy accumulation means, which may be in the form of one, or preferably a pair of accumulators. The connection is preferably made through control means which preferably include a balanced logic controlled manifold that can maintain a constant pressure rating of hydraulic fluid between the pump arrangement and respectively the fluid reservoir and the accumulation means. Additional accumulators can be employed, in particular on a trailer pulled by the prime mover as the energy management system can be applied to the or each trailer pulled. Retardation can be provided by the system, by pumping oil through the control means to the accumulators, or if the accumulator are fully charged or only require partial charge, the oil can be pumped through the control means to the cooling system and then the reservoir with the same retarding effect. In this latter respect, it is not envisaged that the fluid reservoir be pressurised, although that could be achieved if desirable, but instead, the control means can provide resistance to the passage of fluid from the pumping means to the reservoir in the same way than the accumulators provide resistance, and that resistance can be deployed when retardation is required and the accumulators are fully charged.
The, or each accumulator preferably includes a housing, preferably cylindrical, which is closed at either end in a sealed manner and which includes a movable piston within the housing that separates the housing interior into first and second chambers. The first chamber carries a charge of compressible gas, while the second chamber is arranged by suitable valve means to receive and release therefrom, a substantially incompressible hydraulic fluid. The accumulators accumulate energy by increasing the amount of oil stored within the second chamber so that the movable piston is caused to move to reduce the volume of the first chamber and so compress the gas stored therewithin. The fluid is pumped into the second chamber by the pump arrangement when the vehicle is under retardation mode, and in this mode, the drive shaft of the system drives the pump arrangement and it is the load required to drive the pump arrangement that creates the retardation force on the drive shaft. Conversely, when oil is released from she second chamber by the force of the compressed gas pushing the movable piston to reduce the volume of the second chamber, the fluid drives the pump arrangement so that it acts as a motor to drive the drive shaft, so assisting propulsion of the vehicle.
The system can be controlled by a microprocessor that is connected by various sensors to various parts of the system. The microprocessor reacts to information received to govern the operation of the system, in particular, to govern the accumulation and release of energy to/from the accumulation means. The microprocessor can be a programmable logic controller of a simple or sophisticated nature. The controller can alternatively be a computer that can be manipulated manually if necessary.
The present invention further extends to a facility for removing load on the engine of a vehicle, at times when the momentum of the vehicle drives the engine. This occurs normally when the vehicle is traveling downhill when the momentum of the vehicle causes the drive shaft to become driven by the wheels of the vehicle through the differential and that drive causes the engine to be driven at a rate greater than idle, even though the engine is not actually propelling the vehicle. This results in the engine consuming fuel at a rate greater than it would under idle and the fuel consumed is wasted, given that there is no propulsive force generated. All that is generated is a load on the engine which, while it does have a braking effect, also causes consumption of fuel as hereinbefore described and engine wear.
The load removal facility of this aspect of the invention can be provided by a mechanism that disengages the drive shaft from driving the engine, so that the engine can idle under load conditions of the kind described above. This facility can be identified as drive-line separation or DLS. Under the conditions described above and in a vehicle fitted with DLS, the engine consumes fuel at the rate it does under idle, which is the minimum consumption rate available. Any suitable arrangement can be adopted for this purpose and in one form, the mechanism is disposed along time drive shaft, between the engine and the vehicle gearbox. This mechanism includes a disengagable coupling, so that the drive shaft entering the engine can be disengaged from the drive shaft extending to the gearbox. Any suitable disengagable coupling can be employed, and for example, known clutch arrangements could be employed. However, it is preferable that the disengagable coupling be instantly recouplable, as distinct from gradually recouplable, such as is provided with standard automotive clutches that have a pair of opposed clutch faces that are brought gradually into full engagement.
The preferred mechanism employs a selectively engagable clutch that can slip in one direction of drive shaft rotation and which drivingly engages in the other direction. Such a coupling can be arranged to disconnect the separate sections of the drive shaft, when the engine starts to be driven by the drive shaft and to reconnect when engine drive resumes. For this, the mechanism can employ a ratchet-type coupling.
The above described mechanism can therefore operate so that on a downhill run of sufficient incline, the section of the drive shaft extending from the gearbox slips relative to the portion of the drive shaft extending to the engine, so that the latter drive shaft section is not driven and the engine can idle. When the incline begins to flatten out and the momentum of the vehicle reduces, the engine can resume drive of the drive shaft and the coupling between the two sections of the drive shaft will engage by virtue that the section of the drive shaft extending from the engine tends to rotate faster than the section extending to the gearbox.
Preferably the mechanism can be locked against disengagement and any suitable locking means for that purpose may be adopted. In one arrangement, a pin can be employed to lock the disengagable coupling parts together and that pin is preferably insertable through a pair of alignable bores provided in the respective coupling parts. Alternatively, a keyed arrangement may be employed. The pin, if employed, preferably can be inserted and removed from within one or both bores as required to lock or unlock the coupling. Movement of the locking means from a locked to an unlocked position preferably can be manually or automatically activated and any suitable arrangement for that purpose may be adopted.
The load removing facility as above described can be applied to a vehicle independently of the regenerative propulsion system, however they preferably are applied together. In such an arrangement, when the drive shaft is separated, the engine provides no braking effect, (like in a known vehicle such as when the gearbox is placed into neutral) and so the vehicle will tend to accelerate down an incline. To arrest that acceleration, it would be normal to apply the vehicle brakes, however, by application to the vehicle of the energy management system, the vehicle can be retarded without necessarily applying the brakes, or at least with less reliance on the brakes. That retardation can facilitate recharging of the accumulators as previously described, or if the accumulators are already fully so partially charged as appropriate, the retarding energy can simply be dissipated by pumping oil through a controller to the cooling system and then on to the reservoir.
The invention also extends to a terrain logging and prediction facility and that facility employs a memory that memorises the terrain of a certain vehicle route. Thus, the facility memorises the contour of a route, so that in advance, it has knowledge of level and inclined sections of the route and can control the energy management system so that energy can be accumulated and released at the most efficient rate. The facility preferably includes one or more inclinometers suitable to record the contour of the route and a memory, preferably in the form of a computer.
The facility can also be used to log a journey and to provide information either to the driver or to a remote station, as to the position or progress of the vehicle. As such, the facility preferably includes information storage means and transmission means for transmitting data.